Vehicles such as automobiles are installed with an airbag system that may prevent serious injury or death occurring when an occupant comes into contact with a hard part in the interior of the vehicle, such as a steering wheel or a front windshield, during a collision or the like by rapidly inflating a bag with gas to prevent the occupant from contacting such dangerous locations.
An airbag system is preferably capable of restraining the occupant safely, regardless of the body shape (for example, a seated height and so on) of the occupant, the attitude of the occupant (for example, when the occupant is holding the steering wheel), and so on. Accordingly, airbag systems that help ensure that minimal impact is applied to the occupant during an initial activation stage have been proposed in the related art.
In Japanese Patent Application Publication No. 08-207696, gas is generated in two stages such that the airbag is inflated comparatively slowly in the first stage. In the second stage, gas is generated rapidly. For this purpose, two types of gas generating agent capsules are used. As a result, however, the internal structure of the gas generator becomes complicated and the size of a container increases, thus leading to an increase in cost.
[Patent Document 1] Japanese Patent Application Publication No. 08-207696.
U.S. Pat. Nos. 4,998,751 and 4,950,458 similarly propose that an activation function of the gas generator be restricted by providing two combustion chambers such that the gas generating agent is burned in two stages. However, a similar increase in structural complexity occurs in this case, and therefore these proposals cannot be considered satisfactory.
[Patent Document 2] U.S. Pat. No. 4,998,751.
[Patent Document 3] U.S. Pat. No. 4,950,458.
Furthermore, Japanese Patent Application Publication No. 11-334517 discloses a structure for reducing an impact force of the airbag during the initial activation stage by providing a gap in a space that houses the gas generating agent. As a result, however, it is difficult to obtain the initially required amount of gas, and therefore an occupant restraining performance may deteriorate.
[Patent Document 4] Japanese Patent Application Publication No. 11-334517.